A Very Modest Introduction to Streams

What is a Stream? It's Netflix for collections.

forEach

filter

map

Multiplicity Operators

This table shows the multiplicity operators.

Orring

Some Practice Challenges

1. Write a regex that matches a valid decimal integer. Here is a test string. You want to match the first three and not match the second two.

   s = "-243 89 +45 4a3 5.6"

2. Write a regex that matches any alternating sequence of the letters a and b. Here is a test string. The last three should not match.

   s = "ababab a bababa b bab aba baa aab abc"

3. Write a regex that matches any alternating sequence of the letters a, b, and c. Here is a test string. The last four should not match.

   s = "cabcab c a  b bcabcabc ca bc  cba aac cca abcd"

4. Write a regex that matches a 6-digit RGB color code. Be case-insensitive (use a flag).

   s = "0xFFFFCC #FFF8E7 0xaabbcc #aaBBCC #FFFFF #00FF0 0xabc"

5. Write a regex that matches any word containing the vowels a, e, i, o, u in order within the word. Match the first two but not the second two, case insensitive.

    s = "facetiously autoeciously unseriously aeration"

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Challenge
{
    public static void printParseableIntegers(String s)
    {
        Pattern p = Pattern.compile("\\b[-+]?\\d+\\b");
        Matcher m = p.matcher(s);
        m.results().forEach(e -> System.out.println(e.group()));
    }
    public static void main(String[] args)
    {
        //how to stop the period?
        printParseableIntegers("-45 + 56 889 4a5 5.6");
        printABAlternating("ababab a bababa b bab aba baa aab abc");
        printValidHexCodes("0xFFFFCC #FFF8E7 0xaabbcc #aaBBCC #FFFFF #00FF0 0xabc");
        printFiveInOrder("facetiously autoeciously unseriously aeration");
        printAlreadyBeenChewed("cabcab c a  b bcabcabc ca bc  cba aac cca abcd");
    }
    public static void printABAlternating(String s)
    {
        Pattern p = Pattern.compile("\\bb?(ab)*a?\\b");
        Matcher m = p.matcher(s);
        m.results().forEach(e -> System.out.println(e.group()));
    }
    public static void printValidHexCodes(String s)
    {
        Pattern p = Pattern.compile("(0x|[#])[0-9a-fA-F]{6}\\b");
        Matcher m = p.matcher(s);
        m.results().forEach(e -> System.out.println(e.group()));
    }
    public static void printFiveInOrder(String s)
    {
        Pattern p = Pattern.compile("\\w*a\\w*e\\w*i\\w*o\\w*u\\w*");
        Matcher m = p.matcher(s);
        m.results().forEach(e -> System.out.println(e.group()));
    }
    public static void printAlreadyBeenChewed(String s)
    {
        Pattern p = Pattern.compile("\\b(c|bc)?(abc)*(a|ab)?\\b");
        Matcher m = p.matcher(s);
        m.results().forEach(e -> System.out.println(e.group()));
    }
}

Grip.java This program will take two command-line arguments. The first is a file name, and the second is a regex. This program will cause all lines containing a match to the regex to be put to stdout.

Extractor.java This program will take two command-line arguments. The first is a file name, and the second is a regex. This program will locate all matches for the regex in the file and place them in an output file.

public class Extractor
{
    String fileName;
    String regex;
    public static void main(String[] args)
    {
    }
}